My thanks to Pat Ober for this lengthy and helpful email on the
subject of Twain's connection with Kellgren and with Sanna, which is
indeed near Jonkoping, Sweden.  In fact, Sanna is a residential section
of today's Jonkoping.  (My mistake was trusting Google maps, which did
find a town called Sanna--spelled with an umlaut over the first
"a"--near Askersund, at the north end of Lake Vatter.  But there was
nothing at all in that Sanna.)
   With the help of local librarians in Jonkoping, I was able to find
the building in which Kellgren held his clinic.  It is now owned by a
non-profit organization that assists farmers in Sweden.  Included among
their brochures is one that summarizes the history of the building,
including Twain's visit. Unfortunately the house that Twain and his
family occupied no longer exists, though the librarians in Jonkoping
found a picture of it for me.
   Once again, thanks to Pat Ober and others who wrote to me.
                                                 Christopher Morris